Abstract

THOR MATTHEW GOODFELLOW: Androgen Mediation of Elaborate Male Traits: The Effects of Dihydrotestosterone Administration on Vocal Quality in Male Green Treefrogs, Hyla cinerea
(Under the direction of Dr. Christopher Leary)
Elevated androgen levels are well known to mediate the expression of male courtship behaviors and elaborate traits, but whether androgens act via threshold or graded effects is less clear. Models linking elaborate male traits to the endocrine system often assume that androgens have a graded effect on the magnitude or extent of elaborate male traits and that female preference for more elaborate male traits thus drives concordant directional selection on circulating androgen levels. To test this hypothesis, I examined the effects of dihydrotestosterone (DHT) administration on the quality of advertisement calls produced by male Hyla cinerea. Advertisement calls are an elaborate male trait known to be androgen dependent, and females prefer longer calls produced at a faster rate (i.e., high vocal effort) and calls with carrier frequencies that reflect the mean of the population. Analysis of vocalizations prior to treatment indicated that DHT level was not related to call duration, intercall duration, vocal effort, or call carrier frequency. Analysis of plasma hormone levels from blood samples taken before and after treatment showed that DHT injections elevated androgen levels relative to castor oil-injected controls. However, there was no evidence that androgen administration altered call duration, intercall duration, vocal effort, or carrier frequency of the calls of this species. My results thus provide little support for a graded effect of androgens on vocalization in this species. A graded effect of androgens on male sexual signals is central to current models explaining the evolution of elaborate male traits and the endocrine system, but modifications to these models may be necessary.